The plant had been taken offline Nov. 17, so crews could work on two of the five redundant recirculation pumps that are used to move water through the reactor during power operations. They also completed other routine maintenance projects at the facility.

The work could not be performed while the plant is generating electricity.

Oyster Creek is located about 60 miles east of Philadelphia. It generates enough electricity to power 600,000 homes, or roughly all the homes in Monmouth and Ocean counties combined.

The plant went online Dec. 1, 1969, the same day as the Nine Mile Point Nuclear Generating Station near Oswego, N.Y. But Oyster Creek's original license was granted first, making it the oldest of the nation's 104 commercial nuclear reactors that are still operating.

Oyster Creek is due to shut down by the end of 2019 instead of 2029 as called for in its current license.

The plant agreed to the early shutdown in return for not being required to build costly cooling towers that would minimize the impact on fish and other marine life in the creek.